Stirling engine power control means

ABSTRACT

Control of the power in a Stirling cycle engine by means of the control of the volume of working gas is accomplished without loading the pumping mechanism continuously by way of selectively operable valves which connect the pumping mechanism in one position to recirculate gas back into the low temperature chambers from which it is taken and in another position to send the gas from the engine to a storage tank. Another selectively operable valve will permit return of gas from the storage tank to the engine.

United States Patent [191 Bergman STIRLING ENGINE POWER CONTROL MEANS [75] Inventor: Ult Christer Bergman, Malmo,

Sweden [73] Assignee: Kommanditbolaget United Stirling (Sweden) AB & C0., Malmo, Sweden [22] Filed: Nov. 29, 1974 [21] Appl. No.: 528,405

[52] US. Cl. 60/521; 60/525 [51] Int. Cl. F02G 1/06 [58] Field of Search 60/521, 522, 525

[56] References Cited UNITED STATES PATENTS 3,827,240 8/1974 Lundquist 60/521 Oct. 28, 1975 Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney, Agent, or FirmLaurence R. Brown [57] ABSTRACT Control of the power in a Stirling cycle engine by means of the control of the volume of working gas is accomplished without loading the pumping mechanism continuously by way of selectively operable valves which connect the pumping mechanism in one position to recirculate gas back into the low temperature chambers from which it is taken and in another position to send the gas from the engine to a storage tank. Another selectively operable valve will permit return of gas from the storage tank to the engine.

3 Claims, 1 Drawing Figure US. Patent Oct. 28, 19 75 STIRLING ENGINE POWER CONTROL MEANS This invention relates to a double-acting Stirling cycle hot gas engine of the kind (herein called the king defined") comprising a plurality of engine cylinders each receiving a reciprocating piston dividing the engine cylinder into an upper chamber containing gas at a high temperature level and a lower chamber containing gas at a low temperature level, at least one of said pistons being connected to a respectivepiston rod which during operation of the engine reciprocates in the axial direction, a part of said piston rod extending into a respective pump cylinder provided with two check valve controlled gas conduits one of which gas conduits leads from the lower chamber of the respective engine cylinder to said pump cylinder whereas the other gas conduit leads gas away from said pump cylinder.

The piston rods working in the pump cylinders, together with the appertaining conduits and valves, constitute parts of an arrangement whereby it is possible to vary the quantity of working gas employed in the engine in order to vary the power output of the engine.

In an engine of the kind defined it has hitherto been usual to connect the conduit leading from the pump cylinder to a gas storage tank and to include a stop valve in said conduit to stop the gas flow as soon as a predetermined pressure is reached in the tank. Each pump will thus be operating as a piston working on an enclosed amount of gas behaving as a gas spring. Al though the loss in power may be kept within reasonable limits, this involves the drawback that the piston rings working in the pump cylinders will be exposed to severe stresses whenever the engine is operating, even during periods in which the pumps are not pumping gas to the tank.

One object of the present invention is to avoid this drawback. According to the invention there is provided an engine of the kind defined, characterised in that said check valve controlled conduit leading gas away from said pump cylinder contains means for alternatively leading gas into a storage tank or back to the lower chamber of the engine cylinder.

How the invention may be put into practice is described in more detail with reference to the accompanying drawing, showing schematically an engine according to the invention.

The drawing represents the relevant parts of a hot gas engine comprising four cylinders 1 4 each receiving a piston 5 8. The upper part of each cylinder is connected to the lower part of another cylinder via heater pipes 9, a regenerator 10, a cooler 11, and a cold gas connecting duct 12. Only the connecting elements relating to the cylinders 2 and 1 have been provided with reference numerals in the drawing.

The cylinders contain working gas, for example hydrogen or helium, and it will be understood that the shown four-cylinder engine has four separate charges of working gas, each charge being limited by the upper end of a piston in one cylinder and by the lower end of a piston in another cylinder. During operation of the engine each charge of working gas will be cyclically heated and allowed to expand at a high temperature level and cooled and compressed at a lower temperature level.

Each of the pistons 5 8 is provided with a piston rod extending downwardly through the bottom of the cylinder; In the drawing only the piston rod 13 connected to the piston 5 has been provided with a reference numeral. The said piston rod 13 has the shape of a differential "piston with a larger diameter part and a smaller diameter part 14 which extends further downwardly and is connected to a drive mechanism (not shown) forming the engine power output means.

The piston rod 13 extends into a pump cylinder 15 provided with an inlet conduit 16 having a check valve 17 and an outlet conduit 18 having a check valve 19. The inlet conduit 16 is connected to the cold gas'connecting duct 12 and the outlet conduit 18 is connected to a valve 20 having two alternative outlets one being a conduit 21 leading to the space'below the piston 5 in the cylinder 1, the other being a conduit 22 leading to a storage tank 23. v

The storage tank 23 may be supplied with gas delivered from pumps incorporating the other piston rods, similar to the pump described above in connection with cylinder 1.

Gas from the storage tank 23 may be fed to the four engine working gas charges through a common delivery duct 24 including a valve 25 and through branched-off conduits 26 29 each of which comprises a check valve allowing flow of gas only in the direction into the respective cold gas connecting duct.

A further conduit 30 comprising a valve 31 which is adjustable for providing variable resistance against gas flow is able to interconnect all the four low temperature gas working spaces via the branch conduits 26 29 and further branch conduits 32 35. It will be understood that opening of the valve 31 will cause a complete equalising of the gas pressures in the various working chambers in the engine and thus cause the engine to stop. The valve 31 with its short-circuiting effect is known in the art and does not form any part of the invention.

The engine with the power control means as described above and shown in the drawing will operate as follows:

During running of the engine each differential piston consisting of the piston rod 13 and its extension 14 will reciprocate in the cylinder 15, causing flow of gas from the conduit 16 to the conduit 18. In case the valve 20 is in the position shown the gas flow will be directed back through the conduit 21 to the space below the piston 5 in the cylinder 1. Thus there will be almost no pumping work caused by the differential piston l3, 14 due to lack of pressure difference. In these conditions the piston rings or other gas seals between the piston rods and the pump cylinders will not be exposed to severe stresses.

However, if the valve 20 is set into its alternative position in which it connects the conduit 18 with the conduit 22 gas will be pumped into the storage tank 23, and the seals between the rods 13 and the walls of the cylinders 15 will be exposed to normal wear.

As soon as a predetermined amount of gas has been pumped into the tank 23 the valve 20 will be shifted back to the shown position in which the gas pump is relieved of severe stresses.

The valve 25 may be brought into a position in which it connects the delivery duct 24 with the branched-off conduits 26 29, thus causing a flow of gas from the tank 23 into the four low temperature gas working spaces of the engine. As stated above the valve 31 may be used for stopping the engine by short-circuiting all four working gas charges.

What we claim is:

l. A double-acting Stirling cycle hot gas engine comprising in combination, a plurality of engine cylinders each having a reciprocating piston dividing the cylinder respectively into an upper chamber containing working gas at a high temperature level and a lower chamber containing working gas at a low temperature level, a pump operated by at least one said piston to receive working gas at an inlet port and deliver working gas at an outlet port, a first working gas conduit path coupled to said inlet port from the lower chamber of said cylinder containing the last said piston including a one way check valve leading toward said inlet port, a second working gas conduit path coupled from said outlet port including a one way check valve leading away from said outlet port, a valve connected to said second conduit path with means selectively directing the working gas into two paths, storage means in a first of said two paths for receiving said working gas, and a conduit forming the second of said two paths leading back to the lower chamber of said cylinderv 2. An engine as defined in claim 1, wherein each cylinder has a pump and a single storage tank is coupled to receive gas from all the pump cylinders, including a valve selectively actuable to release gas from said storage tank and unidirectional conduits leading from the last said valve to the lower chamber of each of said cylinders.

3. An engine as defined in claim 1, wherein said pump comprises an extension of said piston having a smaller diameter than said cylinders.

l l l 

1. A double-acting Stirling cycle hot gas engine comprising in combination, a plurality of engine cylinders each having a reciprocating piston dividing the cylinder respectively into an upper chamber containing working gas at a high temperature level and a lower chamber containing working gas at a low tEmperature level, a pump operated by at least one said piston to receive working gas at an inlet port and deliver working gas at an outlet port, a first working gas conduit path coupled to said inlet port from the lower chamber of said cylinder containing the last said piston including a one way check valve leading toward said inlet port, a second working gas conduit path coupled from said outlet port including a one way check valve leading away from said outlet port, a valve connected to said second conduit path with means selectively directing the working gas into two paths, storage means in a first of said two paths for receiving said working gas, and a conduit forming the second of said two paths leading back to the lower chamber of said cylinder.
 2. An engine as defined in claim 1, wherein each cylinder has a pump and a single storage tank is coupled to receive gas from all the pump cylinders, including a valve selectively actuable to release gas from said storage tank and unidirectional conduits leading from the last said valve to the lower chamber of each of said cylinders.
 3. An engine as defined in claim 1, wherein said pump comprises an extension of said piston having a smaller diameter than said cylinders. 